Everyone's toooootaally different (as I'm sure you've realised by now!)
This is my first pregnancy too. I'm trying to think back to when I first started to show...but it's hard 'cause I think I thought I looked much bigger than I actually was back then! I've been taking bump pictures every week since I was about 14 weeks and back then I thought I could see a little bump, but when I look back I can't see it at all! Haha.. It totally depends what I wear too. For work I have to wear a dark brown shirt, black pants and a black apron that comes up over my bump, and it's only just started to become noticeable in the last month or so. Only just in the last week have customers started to feel comfortable enough to ask me! But in my own clothes I think it's been relatively obvious since I was about 17/18 weeks..